Influence of Strength Level of Steels on Fatigue Strength and Fatigue Fracture Mechanism of Spot Welded Joints

Abstract

In this paper, quasi-static loading tests and fatigue tests are carried out on spot welded joints of mild steel (270MPa class) and ultra-high strength steel (980MPa class) sheets in order to investigate the influence of strength level of base steels on fatigue strength and fracture mechanism of spot welded joints. Under quasi-static loading, a spot welded part is more liable to be a fracture-initiation site in the ultra-high strength steel than in the mild steel, and as a result fracture behavior of the ultra-high strength steel is considerably affected by a spot welded part as compared with that of the mild steel. Although the fatigue strength of spot welded joints is higher in the ultra-high strength steel than in the mild steel in low cycle fatigue regime, the difference in fatigue strength decreases in high cycle fatigue regime and the fatigue limit is almost the same in both steels. Fracture morphology of spot welded joints under cyclic loading depends on the load level in the ultra-high strength steel, but not in the mild steel. From the comparison between S-N curves for spot welded joints and notched base steels, the dependency of fatigue strength of spot welded joints on base steels is attributed to the notch-sensitivity to fatigue strength of the base steels.

Spot weld arrangement effects on the fatigue behavior of multi-spot welded joints

“…Apart from these parameters, spot weld arrangement in the multi-spot welded joints is a very important and meaningful factor for determining the strength of the joints. The majority of tasks done related to the strengths of the spot welded joints relate to joints with one or two spot weld [12][13][14][15][16][17].…”

The Prediction of Fatigue Crack Initiation Life in Spot Welds

“…All the fatigue test results are available in the previous paper by Tohgo et al. [17]. The Δ σ , Δ τ – N f curves for both tensile and shear specimens are recalled in Figure 6.…”

“…Chemical composition and mechanical properties for the two steels have been listed in Tables 2 and 3 respectively. All the fatigue test results are available in the previous paper by Tohgo et al [17]. The Dr, Ds-N f curves for both tensile and shear specimens are recalled in Figure 6.…”

The Effects of Electrode Force on the Mechanical Behaviour of Resistance Spot‐Welded 5083‐O Aluminium Alloy Joints

“…Resistance spot welding (RSW) technique is the most commonly used assembly process in the automotive industry and other manufacturing fields. Extensive studies have been carried out on the RSW of steel sheets [1–8], but there are little investigations about RSW of other metals rather than steels such as aluminium and magnesium alloys [9–12]. In recent years, there is a strong interest in the use of aluminium alloy sheet for vehicle body because of their advantages such as low weight.…”